Metal turning machine tools such as lathes frequently include a hollow spindle through which bar stock or stock pieces of different diameters are fed to a cutting head. When a stock piece with a diameter less than the inner diameter of the hollow spindle is fed through the spindle, it is desirable to use a spindle liner to constrain the stock piece to a concentric rotation with the spindle, to prevent undesirable wobble or “whip.”
One conventional spindle liner takes the form of a cylindrical reducing tube with an inner diameter and shape configured to slidably receive and support a stock piece, and an outer diameter equal to or slightly less than that of the inner diameter of the spindle. Such a conventional reducing tube is either cast or machined from metal or urethane. Another conventional approach to spindle liners has provided cylindrical tubes with inner diameters for accommodating stock pieces, coupled with annular bearings or O-rings with an outer diameter equal to the inner diameter of the hollow spindle.
These conventional approaches to lining a hollow spindle experience a number of problems. Because of the wide variety of stock piece and spindle shapes and sizes, it can become prohibitively expensive to manufacture a comprehensive set of spindle liners capable of reducing a variety of spindle sizes to a variety of stock piece sizes and shapes. Further, the manufacture of cast spindle liners requires expensive and time-consuming post-cast machining to remove defects and improve tolerances. Further, the mass of conventional spindle liners greatly increases the moment of inertia of the spindle, resulting in additional wear on the spindle and the machine tool. Finally, the nature and extent of the contact area between conventional spindle liners and the spindle may render insertion and removal of the liner difficult.
Accordingly, there is a need for a spindle liner having low production costs, reduced mass, and simplified insertion and removal. The present invention satisfies these needs and provides other advantages as well.